Granite, marble, and similar masonry products are considered to be highly desirable architectural materials for forming the exterior facade or facing of building structures. These materials are not only highly pleasing in appearance, but also very durable and require only a minimum of maintenance. This is borne out by the many marble or granite-faced building throughout the world that were constructed many decades ago and are still in use today. However, the scarcity of marble relative to the current demand and the unprecedented rise in the cost of construction labor have dramatically increased the cost of constructing buildings faced with marble or granite.
In an early construction method, still used today, selected pieces of facing material of marble or granite were hand-set directly on the structural steel skeleton or concrete frame of a building. The panels were held in place by bolts or similar hardware. In this type of construction, the panels of masonry facing material must be at least several inches thick to have the strength necessary to support their own weight without cracking. These panels are not only very costly to quarry and cut to size, but also are difficult to handle if made in a desirably large enough size to cover a building surface within a reasonable length of time. If the height and width of the panels are decreased to make them easier to handle, an increased number of panels are needed to cover the building surface, thereby increasing the number of time-consuming panel-mountings operations required.
Once the marble or granite facade has been attached to the steel or concrete framework or backing, a separate interior wall must be erected. Modern fire codes for commercial structures typically prohibit the use of flame-transmitting materials in the construction of the building walls. In addition, building codes now require that exterior walls be insulated to minimize heat loss in the winter and heat gain in the summer.
In another type of building wall panel, pairs of holes are drilled in the rear sides of the granite or marble panels. C-shaped clips are inserted within the holes and then a layer of glass fiber-reinforced concrete slurry is sprayed over the back surfaces of the granite or marble panels and around the anchor clips to form a solid backing layer. Before the cementitious backing layer sets up, a metal frame is placed over the backing layer and then a second cementitious layer is applied over the first layer and around the components of the frame to join the frame to the first layer. An example of a building panel constructed in this manner is disclosed by U.S. Pat. No. 3,299,601.
U.S. Pat. No. 4,223,502 discloses a building wall panel constructed somewhat similar to that disclosed in U.S. Pat. No. 3,299,601 with the exception that, rather than utilizing a preformed frame, after the cementitious backing layer is spread over the rear surfaces of the masonry panels, integral support ribs are formed from the same slurry material used to form the backing layer, with each rib extending laterally across the back surface of the backing layer. A drawback of this type of wall panel construction is that a significant amount of material and time is required to cover the rear surfaces of the masonry panels with the cementitious material.
In a further type of wall panel construction, a substantially flat rigid plate is sandwiched between individual masonry panels and in a metal backing framework. The individual panels are secured to the backing plate and backing framework by a plurality of anchor studs engaged within blind holes formed in the backsides of the panels. To assemble the building wall panel, the flat plate and metal framework are laid on the backsides of the masonry panels and then holes drilled through the framework and plate and partially through the masonry panels. Studs are inserted through the clearance holes formed in the backing framework and plate and into the blind holes of the masonry panels after a suitable adhesive has first been poured into the blind holes. After the adhesive has set, nuts are engaged on the threaded rearward ends of the studs to join the masonry panels to the backing plate and frame. A disadvantage of this particular type of construction is that additional time and labor are required to form the clearance holes in the backing frame, backing plate, and blind holes in the masonry panels after these components have been placed together. It would be more expedient to perform the holes in the masonry panels and backing framework; however, because of the tolerance involved in locating the preformed holes, it would not be possible to ensure that the slabs are always properly aligned relative to each other and relative to the backing frame. Also, the attaching studs extend perpendicularly to the rear surface of the masonry panels, thereby providing less resistance against pullout than if the studs were skewed or diagonally disposed relative to the slabs. An example of this type of building wall panel is disclosed in U.S. Pat. No. 4,045,933.
U.S. Pat. No. 4,364,212 discloses a building wall panel constructed similarly to that disclosed in the above-described U.S. Pat. No. 4,045,933, with the exception that in the U.S. Pat. No. 4,364,212 patent, oversized blind bores are formed in the individual facing panels. The increased size of the blind bores reduces the strength of the interconnection between the studs and the facing panels.
U.S. Pat. Nos. 4,009,549 and 4,060,951 disclose systems for mounting individual masonry panels to a building framework with rather complicated bracket assemblies composed of a plurality of individual interconnecting brackets that may be adjusted relative to each other to accommodate variations in the locations that mounting openings are formed in the masonry panels. The bracket elements are bolted together by appropriate hardware. One drawback of this type of construction is that if the hardware becomes loosened or workmen neglect to install or properly tighten the hardware, the masonry panels may become detached from the building frame.
Accordingly, it is the principal object of the present invention to provide large building wall panels composed of a plurality of thin masonry panels that are conveniently and securely attached to a metal backing framework that in turn can be directly mounted on a building frame structure.
It is a particular object of the present invention to provide a building wall panel wherein the system for attaching masonry panels to a backing framework is capable of accommodating variations in the locations that mounting holes are formed in the masonry panels.
It is a further object of the present invention to provide a building wall panel wherein hardware attached to masonry panels are interconnected to associated hardware carried on a backing framework through the intermediacy of a bonding medium capable of accommodating variations in the locations of the hardware.